My cali car's beggining to rust

Should I pull it asap? or can it wait a little while, were not talking years or nothing like that just till I can get my hands on some serious grit sand paper. I have sheet metal that I may be able meake a patch out of the only thing I'm worried about is matching the contour I'm not sure if I can get it just right and if I dont it will look terrible.

Shawn.